African Horse Sickness Found in Western Cape

Two horses in South Africa's Western Cape have tested positive for African horse sickness (AHS), reported officials in that area.

According to a public notice issued Friday (March 14) by Dr. John Grewar, state veterinarian (epidemiology) for the Provincial Government of the Western Cape Department of Agriculture Veterinary Services, a private veterinarian tested two horses suspected of having the virus, and those samples came back positive, indicating both horses are positive for serotype 1 AHS. The affected horses reside in the Porterville area, and the source of infection is currently unknown.

Subsequently, the Western Cape state veterinary services developed a containment zone with movement restrictions—meaning no equids can be moved within, out of, or through the specified area.

"The clinical signs seen on the affected property are mild in comparison to previous AHS outbreaks, and no mortalities occurred that have been AHS confirmed as yet," the statement reads. "We thus ask members of the public to be vigilant in their inspection of their horses in the containment area prior to riding or training them as exercising a horse with mild infection may cause the disease to progress faster than expected."

The public notice indicates that there's a "two-pronged approach" to managing this outbreak.

"State officials are undertaking a census and clinical surveillance program in the containment zone starting around the affected property and moving outwards to its borders," the notice reads. "Included in this is informing the public regarding the current state of the outbreak and explaining the containment zone movement requirements."

Additionally, the notice says, "Owners (or owners’ consulting veterinarians) who are informing state officials of suspect clinical cases are being visited and samples are being taken from suspect cases for AHS testing. This includes properties outside of the containment zone."

While there is only one property in the containment zone with confirmed AHS cases, authorities indicate that "there are seven properties within the containment zone where clinical signs which may be associated with AHS are present and where sampling has been performed. Results are pending for these farms."

The state hopes to complete their surveillance and census of the current contamination zone by March 21, the notice says; however, it's not know when control measures will be relaxed.

These aren't the first AHS cases reported in South Africa this year. In late February, Gerrit Van Rensburg, the Western Cape's Minister of Agriculture and Rural Development, issued a statement indicating at least 34 horses have either tested positive for or been suspected of having AHS; 22 of those horses have died, he said.

"Due to persistent high rainfall in the rest of the country the number of cases has increased dramatically and are also occurring earlier than in previous years," Van Rensburg said in the Feb. 28 statement.

As a result, animal health officials have placed restrictions "on all direct horse movements to the Western Cape AHS control area from all other provinces," effective Feb. 28.

South Africa's Department of Agriculture, Forestry, and Fisheries declared the area in the Western Cape an AHS controlled area in 2001, and it includes an AHS-free area to facilitate trade. Horses can be exported directly to the European Union from the AHS-free area. In an effort to protect this area, all horse movements to controlled areas are subject to a state veterinary movement control to prevent introducing the AHS virus into the free zone.

The disease is transmitted by Culicoides midges and does not spread via horse-to-horse contact. Favorable climatic conditions (i.e., summer rainfall) can increase Culicoides breeding and spread. Heavy rains preceded by a prolonged dry spell favor the occurrence of epidemics. The number of outbreaks generally declines after the first frost, and normally the disease occurrence drops abruptly in May.

Veterinarians encourage owners to have their animals vaccinated for AHS before the start of the rainy season to limit the disease's impact. As an extra measure, they advise stabling horses for at least two hours before sunset and keeping them stabled for at least two hours after sunrise, as this is the period when Culicoides are most active and known to be feeding. Culicoides also colonize around stagnant water sources, so try to prevent water pooling and move animals away from water sources such as ponds or lakes.

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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